Base of geometry in learning mathematics which prosecute students to comprehend abstracts things is one of the causes of student difficulties. In this study aims to determine effect of Problem Posing and Problem Solving learning models with the Scientific Approach to students' adaptive reasoning on matter of planes. In this study was organized at the Magetan 4 Junior High School, Indonesia. It employed quasi-experimental research methods. The study population comprised students from grade seventh, with a total sample of 64 students who were divided into 34 student as experimental and other as control classes. Sampling from the population using the simple random sampling method. Normality test uses the Lilliefors method, homogeneity uses the Bartlett test and t-test for analysis of research results. The results showed that the Problem Posing learning model with the Scientific Approach was better than Problem Posing with the Scientific Approach and significantly improved students' adaptive reasoning on the subject matter of the plane. Problem Posing learning models with the Scientific Approach provides the skills needed to build knowledge, where students make the process of observation, clarification, measurement, prediction and make hypotheses. Therefore, the model is very appropriate for learning mathematics, especially on the subject matter of planes to increase adaptive reasoning and students’ achievement.
Keywords: problem posing, problem solving, scientific approach, geometry learning, adaptive reasoning